This invention relates to a cooling system using a semiconductor integrated circuit (IC) device and more particularly to a semiconductor IC device incorporating an abnormality detector for detecting an abnormal condition by using a monitoring signal generated during a system operation.
It sometimes happens that a semiconductor IC device such as a one-chip microcomputer or a DSP behaves abnormally, failing to function according to a prescribed program due, for example, to the noise generated by static electricity. In order to effectively prevent such an abnormal situation, it has been known, as disclosed in Japanese Patent Publication Tokkai 6-110737, to use a monitoring circuit, called a watchdog timer circuit, to detect a runaway situation and to initialize the semiconductor IC device.
A watchdog timer circuit comprises a counter circuit for counting clock signals and serves to reset the counter circuit at a specified timing according to a program when it is functioning normally so as to prevent the counter circuit from overflowing. Under an abnormal or runaway situation, however, the device is not functioning according to a prescribed program and hence the counter circuit may not be reset at an intended timing. Thus, the abnormal or runaway situation may be stopped if the device is initialized by using the signal outputted at the time of such an overflow, and the device can be restored to its normal operating condition.
Although such a prior art method of using a watchdog timer circuit is very effective in the case of a runaway due to an incidental cause, it has not been effective in the case of a constant abnormality of a kind which will cause an erratic behavior even after the semiconductor IC device has been initialized. Moreover, since the user often does not recognize an abnormal condition, such an abnormal condition could cause the destruction of the semiconductor IC device or any apparatus which incorporates it.
One of the examples of abnormality of this kind is due to the heat produced by an apparatus. In an apparatus such as a computer system or a power-supplying system, a semiconductor IC device such as a CPU or a power transistor used within the apparatus generates a significant amount of heat due to the expended power. Thus, without any affirmative effort to cool such a heat-generating semiconductor IC device, it may reach a high temperature beyond its allowable temperature range within which it can be expected to function normally. In order to prevent the occurrence of such a thermal runaway, a cooling device such as an air-cooling fan is used to forcibly cool the semiconductor IC device but if such a cooling device fails to function normally for whatever cause, the temperature of the semiconductor IC device rises gradually, eventually causing a situation of thermal runaway.
With a prior method of using an overflow signal from a watchdog timer circuit, however, a situation of thermal runaway as described above is in most situations not noticed by the user, and the user would fail to investigate or eliminate its cause. Thus, the thermal runaway will start again because the return to the normal condition is only of a temporary nature. If this condition persists, the semiconductor IC device will remain at a high temperature for an extended period of time and, in a worst case, may eventually be destroyed. Even if the user happens to notice an abnormal condition from the behavior of the apparatus, furthermore, the user will not be able to ascertain the situation or to investigate its cause because the semiconductor IC device is automatically initialized after the watchdog timer circuit overflows.
It is therefore an object of this invention to provide a cooling system incorporating an improved semiconductor IC device such that an abnormal condition in the semiconductor IC device of an apparatus using it can be easily detected and that the abnormal condition can be quickly eliminated to prevent the destruction of the apparatus.
A cooling system embodying this invention, with which the above and other objects can be accomplished, may be characterized as incorporating a semiconductor IC device having an abnormality detector for detecting the occurrence of an abnormal condition by receiving clock signals and what is herein referred to as monitoring signals which are outputted intermittently or more or less periodically from a system being monitored. A first gate circuit, or an AND gate, receives the clock signals and generates signals (herein referred to as the count signals) each indicative of a sequentially increasing number, depending on the number of received clock signals or the elapsed time. During a normal operation of the system being monitored, a second gate circuit (or another AND gate) receives the monitoring signals outputted intermittently from the system being monitored. These monitoring signals serve to initialize the increasing counted number. These monitoring signals are received under a normal condition of operation such that the counted number is initialized before reaching a specified value. There is also provided a counter for outputting an abnormality-indicating signal when the counted number reaches the aforementioned specified value. These gate circuits and the counter are so connected that the first gate circuit serves to prohibit input of clock signals, the second gate circuit serves to stop initialization of the counted number when an abnormality-indicating signal is received. With a device thus structured, the output of monitoring signals is not stopped when there is an abnormal condition.